In recent years, advances in technologies have dramatically increased transmission rates and bandwidth in communications networks. Such networks have evolved into what are today known as high-speed networks (HSN's) and are capable of transmitting data at rates on the order of gigabits or even terabits per second. Numerous applications are emerging and attempt to capitalize on an HSN's provision of the enormous bandwidth. Examples of such applications include live video multicasting, multimedia conferencing, high-quality image retrieval, and virtual reality environments.
Because of the extremely high transmission rate requirement, complex network processing by taking advantage of the previous gap between the relatively fast processor speed and relatively slow transmission rate is no longer a reality to HSN's. As a result, a high speed switched network must boost significantly the processing speed of switching nodes to rapidly route the transmitted data therethrough.
A conventional packet switched network is limited in delivering the high processing speed as required. The network nodes in such a packet switched network need to analyze the frame header ofTeach packet in transit to obtain address information in performing routing. The time required for the frame processing is undesirably long.
On the other hand, a conventional circuit switched network does not require the network nodes to perform frame processing. It however requires dedicated circuits for communications between node pairs. This is undesirable in that it neither provides effective bandwidth utilization nor supports efficient interconnection.
Asynchronous transfer mode (ATM) networks are being developed based on the combined concepts of packet switching and virtual-circuit switching. The architecture of one such network is described in: J. Boudec, "Asynchronous Transfer Mode: a tutorial," Computer Networks and ISDN Systems, vol. 24, no. 4, May 1992. ATM network nodes switch cells of information which are identified by the virtual circuit to which they pertain. Before forwarding the ATM cells, a virtual circuit must be established. Thus, among other problems, ATM networks undesirably inherit all the delays associated with circuit establishment, and additional delays resulting from switching the ATM cells to map the virtual circuit identifiers to the appropriate switch input or output ports. In addition, an ATM network undesirably requires that the data entering the network be adapted to an ATM frame structure. As a result, the data needs to be inconveniently converted back into its original protocol before it leaves the network.
Another type of switched networks is known as a wave division multiplexing (WDM) network. The architecture of one such network is described in: A. Acampora et al., "An Overview of Lightwave Packet Network," IEEE Network Magazine, pp. 29-41, Jan. 1989; and C. Brakett, "Dense Wavelength Division Multiplexing network: Principles and Applications," IEEE Journal of Selected Areas in Communications, vol. 8, no. 6, pp. 948-64, Aug. 1990. A WDM network provides dedicated access to destinations via appropriate allocation of wavelengths. Routing is accomplished by configuring nodes to switch the wavelengths to provide source-destination connectivity. Contention among simultaneous transmissions to the same destination are resolved at switching nodes. Desirably, WDM networks may be configured to support circuit-like services and multicasting. However, the implementation of a WDM network is limited to an optical medium and relies significantly upon specialized characteristics of optical transmission. Moreover, in order to realize the high processing speeds at the switching nodes, the network requires optical tuning of switches in the nodes at incoming traffic rates. The optical tuning, as required, is nevertheless beyond the current state of the art. As a result, present WDM networks use dedicated wavelengths between node pairs, and packets may only be sent directly to a neighboring node. At the node, packets need to be processed to determine the destination route, thus undesirably increasing the processing time.
Still another type of switched networks is known as a Highball network. The architecture of one such network is described in: D. Mills et al., "Highball: A High Speed, Reserved-Access, Wide Area Network," Technical Report, 90-9-1, Electronic Engineering Department, University of Delaware, September 1990. In accordance with the Highball network architecture, switching nodes schedule traffic bursts by configuring the switches to support uninterrupted communications. To this end, nodes broadcast requests to all other nodes, specifying their data transmission needs to all possible destinations. This information is then used to determine a schedule at each node and establish time intervals during which output links are dedicated to specific input links. As such, the schedules determined by different nodes must be consistent and the nodes must maintain extremely accurate synchronization. The Highball networks are designed to serve traffic that can tolerate latency delays due to initial scheduling. Thus, the scheduling complexity and the critically accurate synchronization requirement are major shortcomings inherent in the Highball network architecture.
Other prior art networks whose operations rely on substantial traffic multiplexing suffer similar shortcomings. Issues pertaining to these networks such as buffer sizing at intermediate nodes, bandwidth allocation, capacity assignment, and design are resolved based on the assumptions that operations are in equilibrium and traffic demands are originated from a combination of many independent and uncorrelated sources. However, in an HSN a small number of correlated sources may generate correlated traffic comparable to many other sources multiplexed, thus substantially undermining the above assumptions.
In addition, propagation delays in the prior art networks which used to be negligible compared with transmission delays become significant in HSN's. For example, with a cross-country propagation delay of about 30 ms, one can transmit 9 Mbytes through an HSN at 2.4 Gbits/sec. during such a delay. Because of the long propagation delay relative to the transmission delay, conventional protocols based on global feedback for flow control or recovery from loss are no longer effective in HSN's.